Why bypass contactor is using in motor soft starter?
When you install the motor soft starters, you will need to install bypass contactor too. And some motor soft starters is with built-in bypass contactor. Why do motor soft starter need the bypass contactor?
Bypass contactor opens when the motor reaches full speed to reduce power (heat) losses in the solid-state power section. This bings the benefit of much smaller enclosures without need for special cooling.
Bypass contactor significantly reduces heat generated by the motor soft starter. It minimizes enclosure sizes and costs.
With ramp start, the motor is accelerated using an initial torque value of 10 to 85 percent of locked rotor torque, corresponding to 10 to 92 percent of the motor’s locked rotor current. Then the voltage of motor increases over the ramp time. And at 90% of rated speed the built-in bypass contractor closes which reduces voltage drop and cuts heat build up in the starter.
The motor soft starter is an electronic motor starting device. It is intended to provide three-phase induction motors with a smooth start, both mechanically and electrically. Soft starters utilize thyristors in a full-wave power bridge confi guration. By varying the thyristor conduction period, it controls the voltage applied to the motor. Thus it controls the torque developed by the motor. After the motor reaches its designed speed, contactors are closed to bypass the thyristors.
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